Atmospheric Sciences & Global Change Division Research Highlights

January 2005

ARM Observations Validate Climate Model for Tropical Cirrus Clouds

In a study funded by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program, researchers used ground-based observations to assess simulations of tropical cirrus derived from the European Climate Model for Weather Forecasting (ECMWF). As described in Geophysical Research Letters (May 2004) the researchers used lidar and radar measurements of cirrus occurrence obtained between April and November 1999 from ARM's instrumented field site on Nauru Island to assess the accuracy of the ECMWF model in predicting tropical cirrus. Using a subdivided model grid box of 100 independent samples to represent cloud variability, comparisons of cloud top height and optical depth over the eight month period indicated good agreement between the model and measurements. Additionally, both the model and observations showed that tropical cirrus fall into two distinct categories: cirrus near convection (anvils) and cirrus detached from convection.